The invention relates to a gluing apparatus for a labeling machine, consisting of a glue roller, a doctor blade determining the thickness of the glue to be applied, a glue feeder preceding the doctor blade in the direction of rotation of the glue roller, and a glue stripper which can be applied to the circumference of the glue roller.
A frequent source of trouble in labeling stations is the fact that, when the delivery of the bottles is interrupted or discontinuous, the glue pallets continue to take labels from the label magazine even though they cannot be applied for lack of bottles. These unneeded labels pile up somewhere in the labeling station and thus interfere with the application of the following labels after the continuous delivery of bottles has been resumed. To overcome these difficulties, it is known to halt the dispensing of labels from the label magazine if bottle delivery stops. This does eliminate the main source of trouble in the application of labels, but another source of trouble is to be found in the fact that, if the delivery of bottles is interrupted or discontinuous, glue continues to be fed to the glue roll and hence also to the glue pallet. Since no glue is taken from the glue pallets when the label dispensing is halted, the excess glue causes glue to be thrown by the glue pallets, contaminating the labeling station.
To remedy these difficulties, it is known (DE-AS No. 15 86 370, DE-OS No. 26 32 332) to reduce the thickness of the glue coating by a tighter application of the glue wiper so that the glue roller continues to be wetted with glue, but only in such thickness that the glue cannot be flung from the glue roller.
According to the applicant's findings, however, reducing the thickness in which the glue is applied to the glue roller does not in every case suffice to prevent glue from being thrown. For if the pickup element keeps rolling against the glue roller and more glue is constantly added to it, this repeated application of glue will cause glue to collect at the back edge of the pickup surfaces of the pickup elements, and it will be thrown from this point and contaminate the machine.
Another disadvantage of the known machine is that, on account of the need to shift the doctor blade from the disengaged position to the engaged position and back, no matter how precisely it is adjusted in the beginning, in the course of time free play will set in so that the thickness of the glue coating will no longer be precisely controlled in the two positions. On account of this lack of control, the danger exists that in the engaged position too much glue will be applied and in the disengaged position too little glue will be applied, and the glue stripper will engage the glue roller with too much pressure, so that the glue roller with its delicate jacket will overheat.
Any change in the gap between the doctor blade and the glue roller to vary the thickness of the glue coating requires a corresponding change in the adjustment of the throw between the engaged and disengaged position of the doctor blade, and this requires considerable complexity of construction.
There is still another advantage in the known gluing apparatus. When the body and shoulder label and the top foil are to have different thicknesses of glue applied to them, correspondingly different thickness of glue must be transferred to the glue segments. The doctor blade is shaped and adjusted in relation to the glue roller accordingly. When the doctor blade is shifted from the engaged to the disengaged position, it is possible to reduce each of the different glue thicknesses to minimum values. The maximum throw, in other words, is limited by the glue coating having the least thickness. That is to say, it is possible to minimize only one of the coating thicknesses.
In another known gluing apparatus (DE-OS No. 20 59 234) two doctor blades are provided in tandem on the circumference of the glue roller and can be adjusted radially with respect to the glue roller. The glue is fed at the first doctor blade, while its thickness is adjusted with the second. The first doctor blade also serves for the purpose of holding back foreign bodies on the glue roller.
In another known gluing apparatus for a labeling machine (U.S. Pat. No. 4,279,687) it is made possible in the case of an interrupted bottle delivery to completely strip the glue from the glue roller and the glue segments when no labeling is being performed for the lack of bottles. For this purpose a glue stripper is provided ahead of the glue feeder and the doctor blade, in the direction of rotation of the glue roller, and can be pivoted simultaneously with the glue feeder such that, when the glue stripper engages the glue roller, the glue feeder is backed away from the glue roller, and when the glue stripper is backed away from the glue roller the glue feeder engages the glue roller. This known gluing apparatus has the advantage that, in the event of long interruptions, no glue can dry on the glue roller or on the glue segments. If despite the lack of bottles glue is constantly transferred to the glue segments even in a thin coat as in the case of the apparatus known from DE-OS No. 26 32 332, the ability of the glue segments to pick up glue is impaired when the labeling is resumed, with the result that excessively thin or nonuniform glue layers are applied to the labels. Otherwise the known gluing apparatus of U.S. Pat. No. 4,279,687 does not have the above-mentioned disadvantages of other known gluing apparatus.